This weekend, Apple seems to have updated the OS X Mavericks Golden Master (GM) version to a new build. The new build is 13A603 while the original GM seed was 13A598. It’s not common for Apple to change the GM build for a Mac OS, but it is not without precedent. Apple has altered GM iOS seeds before they shipped to customers on a few occasions in the past. Users of the new build have not reported any noticeable user-facing alterations.

The new Mavericks build is not available via the Mac Developer Portal or via Software Update. Instead, it is appearing for users installing OS X Mavericks GM for the first time. Additionally, multiple readers have had success installing the new build by re-installing the Mavericks GM over the 13A598 version. It is currently unclear why Apple felt it necessary to create a new GM build, but it is likely built to squash some remaining bugs. Also unclear: which build Apple plans to actually ship and if this new silent 13A603 release is simply an error.